The present invention relates in general to data processing systems, and more particularly, to a system and method for providing enhanced and peer redundancy modes for local-area network emulation servers in asynchronous transfer mode emulated local-area networks.
Asynchronous Transfer Mode (ATM) is an International Telecommunication Union-Telecommunication Standardization Sector (ITU-T) standard for cell relay in which information for multiple service types, such as voice, video, or data is conveyed in small, fixed sized cells. ATM networks are connection oriented. ATM was originally conceived as a high speed transfer technology for voice, video and data over public networks, but has been extended by the ATM Forum for use over both public and private networks. ATM is a cell-switching and multiplexing technology that combines the benefits of circuit switching with those of packet switching. It provides scalable bandwidth from a few megabits per second (Mbps) to many gigabits per second (Gbps).
An ATM network consists of a set of ATM switches interconnected by point-to-point ATM links or interfaces. ATM switches support two primary types of interfaces. User-Network Interface (UNI) is an ATM Forum specification that defines an interoperability standard for the interface between ATM-based products located in a private network and the ATM switches located within the public carrier networks. Network-to-Network Interface (NNI) is an ATM Forum standard that defines the interface between two ATM switches that are both located in a private network or are both located in a public network. The interface between a public switch and private one is defined by the UNI standard.
When an ATM device wants to establish a connection with another ATM device, it sends a signaling-request packet to its directly connected ATM switch. This request contains the ATM address of the desired ATM endpoint, as well as any Quality of Service (QoS) parameters required for the connection. ATM signaling protocols vary by the type of ATM link, which can be either UNI signals or NNI signals. UNI is used between an ATM end system and an ATM switch across an ATM UNI, and NNI is used across NNI links. A number of connection management method types, including set up, call proceeding, connect, and release are used to set up and break down an ATM connection.
LAN emulation (LANE) is a standard defined by the ATM Forum that gives the stations attached via ATM the same capabilities they normally obtain from legacy LANs, such as Ethernet and Token Ring. The function of a LANE protocol is to emulate a LAN on top of an ATM network and defines mechanisms for emulating either an IEEE 802.3 Ethernet or an IEEE 802.5 Token Ring LAN. The LANE protocol defines a service interface for network layer protocols that is identical to that of existing LANs. The LANE protocol resolves local area network media access control (MAC) addresses to ATM addresses. The LANE protocols operate transparently through ATM switches using only standard ATM signaling procedures. The LANE protocol defines the operation of a single emulated LAN (ELAN).
Each ELAN emulates either an Ethernet or a Token Ring local area network and consists of LAN emulation clients (LEC), LAN emulation server (LES), a broadcast and unknow server (BUS) and a LAN emulation configuration server (LECS). At LEC is an entity in an ATM end system that performs data forwarding, address resolution and registration of MAC addresses with the LES. An LES provides a central control point for LECs to forward registration and control information. There is only one LES for each ELAN. A BUS is a multicast server that is used to flood unknown destination address traffic and to forward multicast and broadcast traffic to clients within a particular ELAN. Each LEC is associated with only one BUS for each ELAN. An LECS maintains a database of LECs and the, ELANs to which they belong. The LECS accepts queries from LECs and responds with the appropriate ELAN identifier, i.e., the ATM address of the LES that serves the appropriate ELAN. There is one LECS that serves all ELANs within its domain. A virtual channel connection (VCC) is a logical circuit that carries data between two end points in an ATM network.
In LANE operation, an LEC first finds the LECS to obtain configuration information. This process starts when the LEC obtains its own ATM address, and typically occurs through address registration. An LEC joins an LES by registering its own ATM and MAC addresses. Once the LEC has joined an LES successfully, it finds the ATM address of the corresponding BUS to join the broadcast group and become a member of the emulated LAN. Actual data transfer between LECs involves resolving the ATM address of the destination LEC.
In the co-pending patent application referenced above, Ser. No. 09/017,306 which is hereby incorporated by reference, a method for providing redundancy to an ATM ELAN is disclosed. The ATM ELAN is served by a primary LES, a BUS, and an LECS. A backup LES/BUS is coupled to the ATM ELAN. A logical redundancy virtual channel connection (VCC), is then established between the primary LES/BUS and the backup LES/BUS. When the redundancy VCC is present between the primary LES/BUS and the backup LES/BUS, the backup LES/BUS is placed in a dormant mode. However, when the redundancy VCC is absent between the primary LES/BUS and the backup LES/BUS, the backup LES/BUS is activated to serve any request generated by the ATM ELAN.
Although the prior invention provided an improved method and system for providing redundancy to an ATM ELAN, it also presents certain shortcomings. A first limitation is the amount of time required to detect the failure of a partner LES/BUS. A second limitation is the disruption incurred as the result of a failure, and subsequent recovery, of the primary LES/BUS.
In view of the foregoing, it is therefore an object of the present invention to provide a method and system for enhancing redundancy to an ATM emulated local-area network.
It is another object of the present invention to provide a method and system for providing peer redundancy to an ATM emulated local area network.
The foregoing objectives are achieved in an Asynchronous Transfer Mode (ATM) emulated local area network (ELAN) served by a primary LAN emulation server (LES), a peer LAN emulation server, a broadcast and unknown server (BUS), and a LAN emulation configuration server (LECS) by establishing an enhanced peer redundancy virtual channel connection (VC) between the primary LES/BUS and the peer LES/BUS. The primary LES/BUS, once started, provides ELAN services to all of its LAN emulation clients (LECs) in the ELAN. It then attempts to establish an enhanced peer redundancy VCC with the peer LES/BUS. If successful, the primary LES/BUS and the peer LES/BUS start exchanging status messages every two seconds that indicate the number of LECs that are assigned to each LES/BUS. If the primary LES/BUS has fewer LECs than the peer LES/BUS, the primary LES/BUS yields to the peer (backup) LES/BUS as the active LES/BUS. The next time through the algorithm, the local LES/BUS is the backup LES/BUS and starts providing ELAN services to all LECs in the ELAN. If an enhanced redundancy VCC had not been established by the primary LES/BUS, then the backup LES/BUS provides ELAN services to all LECs in the ELAN while waiting for the primary LES/BUS to call the backup LES/BUS to establish an enhanced redundancy VCC. In the event that an enhanced peer redundancy VCC cannot be established between the primary LES/BUS and peer LES/BUS, the primary LES/BUS attempts to establish a redundancy VCC with the peer LES/BUS in which the peer LES/BUS is kept in a dormant mode as long as the redundancy VCC is present. If the redundancy, VCC is absent, the peer LES/BUS is activated to service the ELAN.